Field of the Invention
The present invention relates to a lithography apparatus and an article manufacturing method.
Description of the Related Art
In a lithography apparatus such as a semiconductor exposure apparatus, a focus position of a projection optical system may vary due to, for example, a variation in heat generated by exposure light, an atmospheric pressure, an environmental temperature, or the like. It is therefore necessary to calibrate a best focus position periodically before a substrate is exposed. In general, an influence by the above-described variation factor is predicted in advance, and the best focus position is calibrated. For more accurate calibration, however, the best focus position of the projection optical system needs to be measured actually and be calibrated. Conventionally, the best focus position of a projection optical system has been calibrated by measuring a reference mark on an original stage and a reference mark on a substrate stage by a technique such as a TTL (Through The Lens) method (see
In a conventional technique, however, the height position (a position in a Z direction) of the substrate stage needs to be driven actually to measure the best focus position, resulting in a long measurement time. Moreover, measurement accuracy decreases easily if a driving speed is increased under the influence of a vibration caused by driving, making it difficult to shorten the measurement time by increasing the speed of driving. Note that as a focus alignment technique that does not need driving, for example, a general phase difference AF method by a digital camera or the like is considered. However, a spatial resolution in a focal direction is low with this method, making it impossible to achieve a required measurement accuracy.